Department of Pharmacology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA.
J Neurochem. 2011 Nov;119(4):868-78. doi: 10.1111/j.1471-4159.2011.07470.x. Epub 2011 Oct 3.
Traumatic injury to the CNS results in increased expression and deposition of chondroitin sulfate proteoglycans (CSPGs) that are inhibitory to axonal regeneration. Transforming growth factor-β (TGF-β) has been implicated as a major mediator of these changes, but the mechanisms through which TGF-β regulates CSPG expression are not known. Using lentiviral expressed Smad-specific ShRNA we show that TGF-β induction of CSPG expression in astrocytes is Smad-dependent. However, we find a differential dependence of the synthetic machinery on Smad2 and/or Smad3. TGF-β induction of neurocan and xylosyl transferase 1 required both Smad2 and Smad3, whereas induction of phosphacan and chondroitin synthase 1 required Smad2 but not Smad3. Smad3 knockdown selectively reduced induction of chondroitin-4-sulfotransferase 1 and the amount of 4-sulfated CSPGs secreted by astrocytes. Additionally, Smad3 knockdown in astrocytes was more efficacious in promoting neurite outgrowth of neurons cultured on the TGF-β-treated astrocytes. Our data implicate TGF-β Smad3-mediated induction of 4-sulfation as a critical determinant of the permissiveness of astrocyte secreted CSPGs for axonal growth.
中枢神经系统创伤导致软骨素硫酸盐蛋白聚糖（CSPGs）的表达和沉积增加，从而抑制轴突再生。转化生长因子-β（TGF-β）已被认为是这些变化的主要介导者，但 TGF-β 调节 CSPG 表达的机制尚不清楚。我们使用慢病毒表达的 Smad 特异性 ShRNA 表明，TGF-β诱导星形胶质细胞中 CSPG 的表达依赖于 Smad。然而，我们发现合成机制对 Smad2 和/或 Smad3 的依赖性存在差异。TGF-β诱导神经粘蛋白和木糖基转移酶 1 需要 Smad2 和 Smad3，而诱导磷蛋白聚糖和软骨素合成酶 1仅需要 Smad2 而不需要 Smad3。Smad3 敲低选择性降低了星形胶质细胞中 4-硫酸软骨素转移酶 1 的诱导和星形胶质细胞分泌的 4-硫酸化 CSPG 的量。此外，星形胶质细胞中的 Smad3 敲低在促进神经元在 TGF-β 处理的星形胶质细胞上培养时的轴突生长方面更有效。我们的数据表明，TGF-β Smad3 介导的 4-硫酸化诱导是星形胶质细胞分泌的 CSPG 对轴突生长的允许性的关键决定因素。
